[wasm] we should use instantiateStreaming

[kg]

We should try to use https://developer.mozilla.org/en-US/docs/WebAssembly/JavaScript_interface/instantiateStreaming_static to compile and instantiate the runtime WASM module in one step instead of two separate steps. Apparently if you do it in split stages like we're doing now, Safari has to make expensive temporary copies of data and buffer it up. From my profiles of Firefox it may also be beneficial to do instantiateStreaming there too.

This requires some complex internal changes to unify our separate stages into one stage.

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